Interpolymers of the class which include .alpha.-olefin/hindered vinyl monomer substantially random interpolymers and include materials such as .alpha.-olefin/vinyl aromatic monomer interpolymers are known in the art and offer a range of material structures and properties which makes them useful for varied applications, such as compatibilizers for blends of polyethylene and polystyrene as described in U.S. Pat. No. 5,460,818.
As described by D'Anniello et al. (Journal of Applied Polymer Science, Volume 58, pages 1701-1706 (1995)), such interpolymers can show good elastic properties and energy dissipation characteristics. Alternatively, certain of the interpolymers are useful in adhesive systems, as illustrated for instance in U.S. Pat. No. 5,244,996, issued to Mitsui Petrochemical Industries Ltd.
It would be desirable to provide improvements in processability or performance without the addition of additives commonly used to improve properties of the interpolymers or enhance properties that can be achieved by using additives and would be more desirable to achieve combinations of properties not attainable using blends of polymers alone. Alternatively, characteristics of a blend produced to obtain certain desirable characteristics would advantageously be further improved by practice of the present invention. Characteristics which would desirably improve would include at least one of low temperature toughness, mechanical strength, heat resistance and melt processability, preferably heat resistance,
Coupling of polymers results in rheology modification of the polymer. As used herein, the term "rheology modification" means change in melt viscosity of a polymer as determined by dynamic mechanical spectroscopy. Preferably the melt strength increases while maintaining the high shear viscosity (that is viscosity measured at a shear of 100 rad/sec by DMS) so that a polymer exhibits more resistance to stretching during elongation of molten polymer at low shear conditions (that is viscosity measured at a shear of 0.1 rad/sec by DMS) and does not sacrifice the output at high shear conditions.
Use of poly(sulfonyl azide)s to react with polymers is known for instance in The teachings of U.S. Pat. Nos. 3,058,944; 3,336,268; and 3,530,108 include the reaction of certain poly(sulfonyl azide) compounds with isotactic polypropylene or other polyolefins by nitrene insertion into C--H bonds. The product reported in U.S. Pat. No. 3,058,944 is crosslinked. The product reported in U.S. Pat. No. 3,530,108 is foamed and cured with cycloalkane-di(sulfonyl azide) of a given formula. In U.S. Pat. No. 3,336,268 the resulting reaction products are referred to as "bridged polymers" because polymer chains are "bridged" with sulfonamide bridges. The disclosed process includes a mixing step such as milling or mixing of the sulfonylazide and polymer in solution or dispersion then a heating step where the temperature is sufficient to decompose the sulfonylazide (100.degree. C. to 225.degree. depending on the azide decomposition temperature). The starting polypropylene polymer for the claimed process has a molecular weight of at least about 275,000. Blends taught in U.S. Pat. No. 3,336,268 have up to about 25 percent ethylene propylene elastomer.
Similarly, the teachings of Canadian patent 797,917 (family member of NL 6,503,188) include rheology modification using from about 0.001 to 0.075 weight percent polysulfonyl azide to modify homopolymer polyethylene and its blend with polyisobutylene.
It would also be desirable to use a polymer of enhanced melt strength in a foaming process preferably to achieve at least one of smaller cell diameter, homogeneous cell diameter distribution, lower foam density, higher tensile and compressive strength, higher tensile or compressive toughness. Preferably, the polymer would have at most little high shear viscosity increase over a corresponding polymer of the same chemical composition, but not modified to obtain the enhanced melt strength, e.g. the starting material polymer, so that it would have smaller processing characteristics as the unmodified polymer.